AWS Direct Connect and Direct Connect Gateway Scale Limits

by Shahzad Ali
on January 21, 2020

Direct Connect (DX)

  • DX is region specific offering
    • It allows On-Prem physical locations to connect to a specific AWS region/location
  • DX supports max of 50 VIFs (including Private and Public) per physical connection
  • DX does not support Transit VIF for AWS-TGW connectivity

Direct Connect Gateway (DXGW)

  • Only supports Private and Transit VIFs
    • DXGW mainly used to access private resources in VPCs
  • Does not support public VIF
    • DXGW does not provide any benefit of Public Internet Connectivity
  • VGW associated with a DXGW must be “attached” to a VPC
  • Does not support transitive routing or transit connectivity
    • VPC in Region-1 cannot directly communicate with VPC in Region-2
    • DX Location-1 cannot directly communicate with DX Location-2
  • Up to 30 DX physical connections can connect to one single DXGW for physical link redundancy purposes
    • In another words 30 DX locations/regions
  • DX supports max of 50 VIFs (for DXGW only Private and Transit VIFs are applicable)
    • It means one can have Max of 50 DXGW per physical DX link
    • But one DXGW can connect to max of 10 VPCs
    • It means Max of 500 VPCs (50 x 10 VPC) per physical DX link across accounts and regions

DXGW with AWS-TGW Limitations

  • Transit VIF can only be attached to a DXGW
  • Only one Transit VIF for any AWS Direct Connect 1/2/5/10 Gbps connection
    • Less than 1G connections does not support Transit VIF
    • Max of 3 AWS-TGW can connect to one DXGW behind one Transit VIF
  • A single DXGW cannot attach with both Private and Transit VIF
    • This could be a serious limitation for some customers
    • I think the underline assumption is that if a customer is alreadt using AWS-TGW then why would he want to use a private VIF attached to the same DXGW?

DXGW without and with AWS-TGW Comparision

DXGW without AWS-TGWDXGW with AWS-TGW
10 VPCs per DXGW3 TGWs per DXGW
50 DXGW max (b/c of 50 Private VIF)With Transit  VIF only one DXGW is possible
500 VPCs total5,000 VPCs per TGW
15,000 VPC per DX physical link
Private VIF supported on all Direct Connect connection typesTransit VIF supported only on dedicated or hosted connections of speed 1Gbps and above
No additional chargesAdditional charge for TGW data processing

References

https://docs.aws.amazon.com/vpc/latest/tgw/transit-gateway-limits.html
https://docs.aws.amazon.com/directconnect/latest/UserGuide/limits.html

Credits

Abdul Rahim
Kamran Habib
Saad Mirza
Hammad Alam

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